Exemplary embodiments of the present invention relate to the production of fiber composite components, and particularly to a device and method for the infiltration of fibrous material with resin for the production of a fiber composite component. In addition, the invention relates to a use of such a device and/or such a method.
Very generally speaking, it is important for achieving high quality in fiber composite components that the resin impregnate the fibrous material as evenly as possible during the resin infiltration process. For this purpose, the use of so-called “flow promoters” is known in the prior art. Such flow promoters, which are included together with the fibrous material being infiltrated in an infusion structure, are typically structures used to facilitate a rapid and/or particularly even distribution of resin in the fibrous material and/or along at least one side—e.g. the flat side—of the fibrous material. The idea of this approach is that the applied resin becomes particularly quickly distributed in the flow promoter due to the low flow resistance of the flow promoter (e.g. large-meshed textile sheets, screen-like woven materials, etc.), such that the resin distributed in the flow promoter can then penetrate further into the fibrous material “by the short route” via the corresponding boundary surfaces and/or surfaces of the fibrous material.
A device in the class and a method in the class are known from DE 101 57 655 B4.
In the known device, a mold tool is used for the infiltration of a preform (fibrous material) with resin, wherein a cavity is enclosed by at least two tool parts which are able to move toward each other but are still sealed against each other, to then hold the preform. The mold tool is designed in such a manner that space can be provided inside the cavity, in a first tool position, to hold the preform, and “additional space” can be provided to accommodate added resin. The cavity can then shrink as a result of a movement of the mold tool from the first tool position into a second tool position, in order to press the resin which remains in the additional space of the cavity, following the resin infiltration, like a wedge from this additional space into the preform.
This approach advantageously allows an economic production of fiber composite components without waste (“excess resin”).
In this prior art, rather than a flow promoter, an “additional space” is provided in the mold tool (the column above and below the fibrous material being impregnated) during the infiltration process.
However, it is a disadvantage in this prior art that, particularly when the resin feed rate is comparable, there is a risk of undesired deformations and/or movement of fibers in the adjacent fibrous material during the infiltration process—particularly during the filling of the “additional space” in the tool cavity.
Proceeding from this prior art, the problem addressed by the present invention is that of avoiding the named disadvantage, and particularly of providing a device and a method for the infiltration of fibrous material with resin which enable a comparably fast impregnation of the fibrous material with a comparably low risk of fiber movements.
The device according to the invention is characterized in that a flow promoter is included in the cavity, comprising at least one first layer and one second layer, connected to each other in an edge region of the flow promoter to enclose a flow space, wherein the first layer is impermeable to resin while the second layer provides an outlet for guiding resin out of the flow space and into the fibrous material, and wherein the flow space of the flow promoter is filled with resin and/or the flow promoter has an inlet for conveying resin into the flow space.
The method according to the invention is accordingly characterized in that it also comprises the following steps:                arranging a flow promoter in the additional space of the cavity, wherein the flow promoter has at least one first layer and one second layer, connected to each other in an edge region of the flow promoter to enclose a flow space of the flow promoter, wherein the first layer is impermeable to resin while the second layer provides an outlet for guiding resin out of the flow space and into the fibrous material, and wherein the flow space of the flow promoter is filled with resin and/or the flow promoter has an inlet for conveying resin into the flow space, and        optionally conveying resin into the flow space of the flow promoter, such that resin is pressed out of the flow space of the flow promoter and into the fibrous material when the mold tool is moved from the first tool position into the second tool position.        
One aspect of the invention is therefore that of deliberately using, in contrast to the intended use thereof, a so-called “flow promoter” in applications of a device in the class, and/or a method in the class—even though the construction of the device and/or the functionality thereof “actually” makes such a flow promoter unnecessary (cf. DE 101 57 655 B4 named above, paragraphs 0002, 0003, and 0013, for example)—to thereby be able to advantageously better control the penetration of the resin into the fibrous material during the infiltration process—and nevertheless not for the purpose of achieving an improved distribution of resin.
According to the invention, undesired fiber movements are prevented by the use of the flow promoter which is arranged in the “additional space” inside the cavity of the mold tool, and provides an “outlet” (which can be optimally adapted to the specific application, by way of example) for guiding resin out of the flow promoter and into the fibrous material.
Because the resin must pass through this outlet in order to penetrate into the fibrous material, it is possible to specifically ensure, by means of a corresponding design of the outlet, that the resin conveyed to the additional space and/or the flow promoter in this additional space is not able, by way of example, to penetrate immediately into the fibrous material entirely unhindered, and (particularly where high injection pressures and/or volume flows are used) result in displacements of the fibers.
The flow promoter, which can have any shape and size in principle within the scope of the invention, preferably is of a flat, elongated, plate- or pillow-like form. Particularly in this case, the flow promoter can be and/or is arranged in the device and/or in the method with one flat side, formed by the second layer, flush against a flat side of a fibrous material which is flatly elongated as a whole.
The “first layer” of the flow promoter is impermeable to resin. This includes any layer through which the resin is not able to pass—even under the temperature and pressure conditions which are adjusted to functionally match the particular application situation.
The term “resin” in the context of the invention is used to indicate a material which is suitable for forming a fiber composite component with a fibrous material. This material (matrix material) can also contain a curing agent, by way of example (as a multi-component resin system). “Resin” in the narrower sense of the word refers to thermosetting plastics such as epoxide resin systems. However, all thermoplastic duromers, by way of example, should be included.
The “second layer” of the flow promoter provides the above-noted outlet for the resin. The term “outlet” in this case means a single opening, or preferably a plurality of openings, through which the resin can exit, particularly when there is an overpressure (with respect to the pressure on the other side of the outlet—that is, the space in which is found the fibrous material being infiltrated).
In one embodiment, the outlet of the second layer is provided by a perforation in the second layer and/or by a permeability to resin, produced by the material itself, in the second layer.
The outlet preferably comprises a plurality of openings (perforations) which are configured in the second layer in such a manner that it is possible to press the resin into the fibrous material at many points without the resin needing to flow over greater distances through the fiber material.
The two layers of the flow promoter named above can be formed from a film material and/or a textile material, by way of example. In one embodiment, the first layer is made of a film material (preferably of plastic), and the second layer is made of a textile material. As an alternative, the second layer can also be made, by way of example, of a film material which is nevertheless suitably perforated, for example.
In one embodiment, the device according to the invention also comprises resin feed means for the purpose of feeding resin into the flow space of the flow promoter. Such resin feed means can include, by way of example, one or more channels in the region of the at least two tool parts, wherein resin can be allowed to flow through the same into the flow promoter (for example via a tube which connects the opening of such a channel in the cavity with the inner space (flow space) of the flow promoter).
As an alternative to such a feed of resin via resin feed means of the device, it is also possible within the scope of the invention that a flow promoter which is filled in advance with resin is arranged in the cavity of the mold tool together with the fibrous material. In this case, with the flow promoter laid in place (and already filled), there is no need for a subsequent feed of resin into the flow space of the flow promoter.
The second layer of the flow promoter can possess, by way of example, advantageous separating properties with respect to the resin used (for example as the result of a corresponding surface treatment or coating) in order to make it possible to easily separate the flow promoter from the cured fibrous material after the infiltration process and/or the production of the fiber composite component is complete (by, for example, thermal curing of the infiltrated fibrous material).
In one embodiment of the invention, a perforated separating film and/or a so-called peeling sheet is used between the flow promoter and the fibrous material.
As an alternative, however, it is possible within the scope of the invention to leave the flow promoter on and/or in the finished fiber composite component following the completion of the infiltration process. In this case, the use of, by way of example, a material for the two layers, said material breaking up and/or dissolving in the resin used—for example to achieve an intended modification of the resin properties at the affected component interface and/or surface—can be contemplated.
The second layer of the flow promoter, which faces the fibrous material, can have properties such that it is not permeable for the matrix material at low differences in pressure (e.g. up to about 1 bar), but becomes permeable once a certain pressure difference is exceeded (e.g. 2 bar) (for example due to a microporous material structure of the second layer). As an alternative or in addition thereto, a permeability and/or a significantly elevated permeability can also be created by a certain temperature being exceeded by the resin (that is, by passing beyond a certain (temperature dependent) viscosity of the resin).
A further possibility for creating permeability in the second layer for the resin in the specific application during the production process is that of designing this second layer in such a manner that regions of the second layer melt when a certain temperature is exceeded (whether that be as a result of the feed of resin, for example, or as a result of the tool being heated for this purpose, for example).
In one embodiment, the device further comprises air discharge means to discharge air from the cavity. These air discharge means can also comprise, by way of example, channels which are constructed in the region of the at least two tool parts (passing through at least one of these).
In this context, it is advantageous if the mold tool is designed in such a manner that the cavity can be closed in an airtight manner—particularly such that this airtight configuration can be maintained in both the first tool position and the second tool position, as well as during a movement between these two tool positions. For this purpose, there can be a compressible seal inserted by way of example in a gap on the edge of the two tool parts, running around the same, becoming accordingly compressed and/or elongated when the two tool parts move toward each other or away from each other, and thereby ensuring an airtight seal of the edge gap between the tool parts. As an alternative or in addition thereto, tool parts which are able to move with respect to each other can also be sealed by direct contact with each other.
The two layers of the flow promoter can be connected to each other in their edge region in a variety of ways. The layers are preferably welded, glued, or sewn together in the edge region, and a combination of these connection types can also be used. The edge region therefore preferably has a weld seam, a glue seam, and/or a sewn connection. This connection is preferably constructed running around the periphery, although there can also be an interruption at least at one position of this contour in order to form and/or allow the passage of the inlet of the feed of resin into the flow space at this point.
According to one embodiment, the two layers of the flow promoter have already been connected to each other during the production of the flow promoter (e.g. by welding).
As an alternative, the flow promoter could also have separate layers (e.g. films) which are inserted into the respective mold tool and then connected to each other at that time—for example running laterally outside of the fibrous material edge together toward a lateral edge of the tool, and being connected to each other there (e.g. by gluing or by being pressed against each other by means of a peripheral seal and then pressed against a tool part surface). In this case, the “connection of the layers to each other in an edge region of the flow promoter” would only take place during the application.
The fact that the two layers are connected to each other “in an edge region of the flow promoter” does not necessarily mean that this edge region also constitutes an edge region of the two layers. Rather, at least one of the layers can extend beyond said “edge region of the flow promoter” (cf. the examples according to FIGS. 3 and 5 described below, for example).
In one embodiment, the first layer of the flow promoter is impermeable to resin, but allows the passage of air, and the flow promoter also comprises a third layer which is impermeable to resin, impermeable to air, is arranged on the side of the first layer which faces away from the second layer, and is connected to the first layer in the edge region of the flow promoter. In this construction, when air is suctioned out of the intermediate space between the first and third layers by means of a suitable means, the space of the cavity which surrounds the flow promoter can advantageously be evacuated as a result of the first layer allowing the passage of air—said space particularly also being the space assumed by the fibrous material. Then, resin can be introduced via the inlet of the flow promoter which opens into the flow space (between the first and second layers). In the process, the negative pressure between the first and third layers facilitates the evacuation of the flow space.
In one embodiment of the infiltration method according to the invention, the fibrous material and the flow promoter are first arranged in the cavity of the mold tool, then the resin is conveyed into the flow space of the flow promoter by means of resin feed means of the device. Finally, the size of the cavity is reduced by an adjustment of the mold tool from the first tool position into the second tool position, such that resin is pressed out of the flow space and into the fibrous material via the outlet provided by the second layer, as a result of this adjustment. As mentioned above, however, it is also possible for the flow promoter, already filled with resin, to be arranged in the cavity of the mold tool, thereby rendering the step of feeding resin unnecessary.
In one embodiment, substantially more space is available inside the cavity to accommodate the fibrous material after the movement of the tool into the second tool position.
According to the invention, the device described and/or the method described are preferably used to produce a plate-like or cup-like fiber composite component. In the simplest case, such a fiber composite component is a single- or multi-layer fibrous material laminate. However, within the scope of the invention, fiber composite components can be produced which are formed of multiple layers—partly of fibrous material and partly of another material. So-called sandwich components are one example of this. There are at least three layers in a sandwich component, typically termed a core layer and cover layers (arranged on both side of the core). In such a construction, the invention can be used, by way of example, for the purpose of connecting these three layers to each other in a mold tool, thereby achieving an infiltration of each of the cover layers made of fibrous material. In this case, a foam layer, preferably closed-cell foam, can particularly be used as the core layer, for example. As an alternative, a so-called honeycomb structure (e.g. of paper, cardboard, plastic, etc.) can also be used, by way of example. In the latter case, it is advantageous if the honeycomb structure is utilized with a seal on the end-face thereof (e.g. with honeycomb structure cover layers which are impermeable to resin), in order to prevent the honeycombs from filling up completely with resin in an undesired manner.
The following advantages are achieved in particular in the production of fiber composite components using the invention:                faster distribution of the matrix materials (resin) and impregnation of the fibrous material (for example provided either dry or as a pre-impregnated preform), with accordingly shorter cycle times and/or the ability to use more reactive resin systems (e.g. epoxide resin systems; wherein thermosetting plastics can also be contemplated, for example) and/or matrix systems with higher viscosity (e.g. rubberized systems),        avoidance of fiber displacements even at high resin injection pressures and/or volume flows,        an optimization of the resin filling process does not require any, or any significant, changes to existing mold tools (e.g. the position(s) of the injection point(s)). Rather, an adaptation of the properties of the “outlet” of the flow promoter (e.g. the pattern of perforations) is generally sufficient to enable shorter development times and lower development costs, and to easily implement component or process modifications.        depending on the embodiment, the difficulty of cleaning the mold tool following the production of a fiber composite component is reduced, or the cleaning is eliminated.        